A gas turbine engine comprises a plurality of rotating elements, such as shafts, rotating at a very high rotation speed when the engine is running. These rotating elements are supported by bearings provided at various strategic locations in the engine. These bearings are lubricated using pressurized oil. Oil is sent to the bearing cavities using oil pumps that are mechanically driven and as a result will start to pump oil to the bearings as soon as the engine starter is engaged. One drawback is that when starting the engine or during the run down, the air-oil seals of bearing cavities are inefficient because of the lack of sufficient air pressure. This may result in oil leaks, which is undesirable.